Determination of wheel sensor position using radio frequency detectors in an automotive remote tire monitor system

ABSTRACT

In a remote tire monitor system, radio frequency (RF) signals including tire data are transmitted from a plurality of tire monitors at wheels of a vehicle. At an RF receiver, the signals are received and tire data is detected. The RF signals are detected at a receiving RF detector associated with the transmitting tire monitor. The receiving RF detector produces a transmission indication in response to the received RF signals. A control unit is coupled to the RF receiver and the RF detector. The control unit receives the tire data and the transmission indication and associates a position of the transmitting tire monitor with the tire data in response to transmission indication. This permits automatic update of the position of tire monitors on the vehicle.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to a remote tiremonitoring system. More particularly, the present invention relates to amethod and apparatus for automatically updating position information fortire monitors in such a system.

[0002] Systems have been developed to monitor a characteristic such astire pressure of a vehicle and to report the characteristic to areceiver at a central monitoring station using radio transmissions. Amonitor is located at each tire and periodically takes a measurement ofthe tire characteristic. The monitor then transmits the results of themeasurement in a radio frequency transmission to the central monitoringstation which produces an alarm or a display in response to themeasurement.

[0003] One problem with such systems has been the need to program thelocation of the transmitters at the central station. To be fully useful,the tire characteristic data is preferably associated with the tirewhich originated the measurement when presenting a display or alarm.Each monitor includes identification information which can betransmitted with the measurement. The tire monitor is preferablyactivated to produce this information and the information is thenconveyed to the central station and associated with the position of thetire.

[0004] In the technique of U.S. Pat. No. 5,600,301, the tire monitorseach include a reed switch or other magnetic device. A magnet is passednear the reed switch, causing the monitor to transmit a radio frequencytransmission that includes identification data. A service technicianrepeats this process at each wheel and then loads the identification andposition information into the central monitoring station. Another methodprovides a printed bar code on each tire monitor which contains theidentification information and which may be read with a suitable barcode reader.

[0005] In U.S. Pat. No. 5,880,363, an activation signal is provided fromthe central controller to a low frequency transmitter at each wheelwell. The transmitter generates a low frequency signal to activate thetire monitor. The tire pressure monitor responds by generating a longwave identification signal and transmitting that signal with tirepressure and identification data directly to the control unit. The longwave identification signal is used to identify the position of the tireby distinguishing this transmission from other transmissions received bythe controller.

[0006] U.S. Pat. No. 5,883,305 discloses two-way communication of databy radio signals. A tire pressure monitor is activated by a radiofrequency signal transmitted by an antenna in the wheel well adjacentthe tire. The tire pressure monitor transmits a second radio frequencysignal which is detected by the wheel well antenna. The second signal isdemodulated to detect that tire pressure data.

[0007] These previous techniques have been limited in effectiveness. Themagnetic programming technique may be subject to interference andcrosstalk, for example in a factory where many such tire monitors arebeing assembled with tires and vehicles. The bar code label systemrequires a label at each tire which can be lost or become dirty orillegible. The apparatus for transmitting a long wave activation signaland generating a long wave identification signal therefrom is tooexpensive for some applications. The two-way data communicationtechniques requires demodulation of the received radio signals at thewheel well and coaxial cabling back to the central controller, both ofwhich add to the cost of the system.

[0008] A further limitation of some of these prior techniques is themanual operation requiring activation by a service technician. A systemis desired which automatically conveys wheel position data to thereceiver. Such a system would be particularly useful after any change intire position, such as tire rotation or replacement of a tire.

SUMMARY

[0009] By way of introduction only, a remote tire monitor method andapparatus provide a central control unit in the cockpit or trunk of avehicle. The control unit includes a radio frequency (RF) receiver and acontroller. Tire monitors are located at each wheel of the vehicle andperiodically transmit tire data such as tire pressure information, alongwith a tire monitor identifier. Four small, inexpensive RF detectors arelocated near each wheel, for example, in the wheel well. Each detectoris connected to the central control unit by a power line and a groundline.

[0010] When a tire monitor transmits data by emitting an RFtransmission, the RF detector that is closest to the transmitter willdetect the burst of RF energy. The RF detector responds to the RF energyby modulating the power line to the control unit with the envelope ofthe transmitted data. The control unit detects this modulation on one ofits power lines. Also, the RF receiver of the control unit receives anddemodulates the data transmitted by the tire monitor. The control unitassociates the received data with the position indication provided bythe modulation on the power line. When the positions of the wheels onthe vehicle are changed, the control unit can determine the new positionusing the modulated power line or by using the tire monitor identifierin the transmitted data.

[0011] The foregoing discussion of the preferred embodiments has beenprovided only by way of introduction. Nothing in this section should betaken as a limitation on the following claims, which define the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWING

[0012]FIG. 1 is a block diagram of a remote tire monitor system shown inconjunction with portions of a vehicle;

[0013]FIG. 2 is a flow diagram illustrating an auto learn method for theremote tire monitor system of FIG. 1; and

[0014]FIG. 3 is a flow diagram illustrating an auto learn method for theremote tire monitor system of FIG. 1.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0015] Referring now to the drawing, it is a block diagram of a remotetire monitor system 100 shown in conjunction with portions of a vehicle102. The vehicle 102 includes in this example four tires 104. Othernumbers of tires may be included, such as a fifth tire as a spare oradditional tires if the vehicle is a truck, trailer or othermulti-wheeled vehicle.

[0016] Associated with each of the tires 104 is a transmitter or tiremonitor 106. Each of the tire monitors 106 includes a battery powered,radio frequency (RF) transmitter. Any suitable tire monitor may be used.U.S. patent application Ser. No. 09/245,938, entitled “Method AndApparatus For A Remote Tire Pressure Monitor System,” filed Feb. 5, 1999in the name of McClelland et al., and commonly assigned with the presentapplication is incorporated herein by reference and illustrates onesuitable tire monitor for use in the remote tire pressure monitor system100. Each tire monitor 106 includes a sensor such as a pressure sensorfor measuring a tire characteristic. The tire monitor 106 converts themeasured tire characteristic to tire data. The tire data is encoded fortransmission from the tire monitor 106.

[0017] The tire monitor further includes a transmitter configured totransmit RF signals including the tire data. In some embodiments, thetransmissions are encoded or randomized to minimize clashes at areceiver. For example, U.S. patent application Ser. No. 09/245,577,entitled “Method For Communicating Data In A Remote Tire PressureMonitoring System,” filed Feb. 5, 1999 in the name of Bailie, et al.,and commonly assigned with the present application is incorporatedherein by reference. This application shows a technique in which datawords are transmitted separated by a time delay. The time delay for eachrespective data word is defined according to a repeating pattern commonto the tires so that data words are transmitted during a plurality ofaperiodic time windows. Transmission parameters such as modulationtechniques, transmission frequency and transmission power are chosenaccording to local regulations and to assure reliable reception of theRF signals.

[0018] The tire monitor 106 includes a motion switch 139. The motionswitch 139 closes upon detection of movement of the vehicle 100. Themotion switch 139 provides a signal to the processor 124 indicatingclosure of the switch 139 and motion of the vehicle. In response toclosure of the switch, the tire monitor system 100 begins operating, forexample, by transmitting tire data. In the illustrated embodiment,during normal operation, the tire monitor 106 transmits supervisory tirepressure information once every minute. Any suitable motion switch maybe used for the switch 139.

[0019] The remote tire monitor system 100 includes a control unit 110and a plurality of radio frequency (RF) detectors 112. In alternativeembodiment, the remote tire monitor system 100 additionally includes auser display for providing user information such as tire pressureinformation and low tire pressure alarms. In the illustrated embodiment,each RF detector 112 is mounted on the vehicle 102 proximate anassociated tire monitor 106 to detect the RF signals from the associatedtire monitor 106 and produce a transmission indication in response todetected RF signals. Each of the RF detectors 112 is electricallycoupled by a conductor 114 to the control unit 110. Structure andoperation of the RF detectors 112 will be described in greater detailbelow.

[0020] The control unit 110 includes an RF receiver 120, an RF decoder122, and a controller 124. The RF receiver 120 is configured to receiveRF signals conveying tire data from at least one transmitting tiremonitor 106 of the plurality of tire monitors 106 associated with thewheels or tires 104 of the vehicle 102. Any suitable RF receiver circuitmay be used. The design and implementation of the RF receiver 120 willdepend on the type of modulation used for the RF signals, transmissionfrequency for the RF signals, and physical limitations such as permittedsize, weight and power dissipation.

[0021] The RF decoder 122 is configured to receive a transmissionindication from at least one receiving RF detector 112 of a plurality ofRF detectors 112 associated with wheels or tires 104 of the vehicle 102.Thus, a tire monitor 106 will transmit RF signals which are detected bythe RF detector 112 associated with the transmitting tire monitor 106.The receiving RF detector 112 signals its detection of the RF signals byproviding the transmission indication on its associated conductor 114.

[0022] The RF decoder 122 is further configured to identify a positionof a transmitting tire monitor on the vehicle in response to thetransmission indication received from an RF detector. Accordingly, theRF decoder 122 includes a plurality of input circuits 123 coupled to theconductors 114 which are in turn coupled to the RF detectors 112. Atransmission indication impressed on a conductor 114 is detected by anassociated input circuit 123. In the illustrated embodiment, there is aone-to-one relationship between input circuits 123 and RF detectors 112.In this manner, the RF detector 112 which originated the transmissionindication may be identified by the RF decoder determining which inputcircuit 123 detects the transmission indication. In alternativeembodiments, the RF decoder 122 may include fewer than four inputcircuits 123 which are multiplexed in some manner among the plurality ofRF detectors 112. For example, a single input circuit 123 may be timeshared among the plurality of RF detectors 112 to reduce the cost andcomplexity of the RF decoder 122.

[0023] The RF decoder 122 is electrically coupled with the RF circuit120. Upon receipt of RF signals at the RF circuit 120, the RF signalsare demodulated to extract the tire data contained within the RFsignals. In some applications, additional data decoding may be requiredafter demodulation. The tire data in one exemplary embodiment includes atire monitor identifier, or unique identification code which uniquelyidentifies the tire monitor 106 which transmitted the RF signals. Inaddition, in this exemplary embodiment, the tire data also includes tirepressure data related to a sensed tire pressure of the tire 104 at whichthe transmitting tire monitor 106 is located. Alternative tire data maybe included or substituted for the tire pressure data, such as a numberof tire revolutions, tire temperature, and so forth.

[0024] After extracting the tire data from the RF signals, the tire datais conveyed from the RF receiver 120 to the RF decoder 122. The RFdecoder 122 associates the tire data with a position of the transmittingtire monitor 106 on the vehicle 102. Position information is determinedusing the input circuit 123 and a transmission indication received overa conductor 114 from RF detector 112. The tire data and associated tireposition are conveyed from the RF decoder 122 to the controller 124.

[0025] The controller 124 controls the operation of the remote tiremonitor system 100. The controller 124 is preferably a microcontrollerincluding a processor 128 and a memory 126. The processor 128 operatesin response to data and instructions stored in the memory 126 to controloverall operation of the system 100.

[0026] In the illustrated embodiment, the processor 128 stores positiondata for a plurality of tire monitors 106 of the remote tire monitorsystem 100. The controller 124 is electrically coupled to the RF decoder122 to receive tire data and position data from the RF decoder 122. Inthe illustrated embodiment, when tire data and position data arereceived at the microcontroller 124, the processor 128 retrieves storedposition data from the memory 126. In one embodiment, the position dataare stored in association with a position on the vehicle, such as leftfront, left rear, right front or right rear. The received position datais compared with the stored position data. If there is no change, theposition data is not updated and further processing may occur using thereceived tire data. However, the processor 128 updates the position datafor the transmitting tire monitor 106 when the position of thetransmitting tire monitor 106 varies from the stored position data forthe transmitting tire monitor. Thus, the controller 124 includes amemory 126 and a processor configured to store in the memory 126position of the plurality of tire monitors 106 including the position ofthe transmitting tire monitor which originated the received positiondata.

[0027] In an alternative embodiment, the memory 126 is not used forstorage of position data. Rather, the received tire data is associatedby the control unit 110 with the position information provided by thetransmission indication from a RF detector 112. The tire data and theposition information from the input circuit 123 are used together toproduce a display or alarm, if appropriate, by the system 100.Additionally, in still another embodiment, the tire data omits anyidentifying information for the transmitting tire monitor 106 and again,the tire data and the position information from the input circuit 123are used together to produce the appropriate display or alarm.

[0028] Completing the identification of the elements in FIG. 1, thevehicle 102 further includes a CAN driver 130, a voltage regulator 132,power line noise suppressor 134, and a battery 136. The battery 136provides operating power for electrical systems of the vehicle 102including the remote tire monitor system 100. The battery 136 is aportion of the electrical power system of the vehicle, which typicallyalso includes an alternator and other components. Such electrical powersystems for vehicles are well known. The power line suppressor 134reduces noise on the power line from the battery 136. Noise mayoriginate in other electrical components of the vehicle 102, such as theignition system. The voltage regulator 132 receives the battery voltageor other operating voltage from the power line suppressor 134 andproduces a well regulated voltage for components such as the controlunit 10 and CAN driver 130. The CAN driver 130 provides electricalinterface with other elements of a Controlled Area Network. ControlledArea Network or CAN is a serial communication protocol for data commonlyused in automotive and other applications. The CAN bus 138 accessed bythe CAN driver 130 is used to interconnect a network of electronic nodesor modules. The CAN bus operates according to an adopted standard. Inconjunction with a remote tire pressure monitor system 100, the CAN bus138 may be used to convey tire monitor data to other locations in thevehicle 102. For example, an alarm or a display (not shown) may becontrolled to provide a visual or audible indication to an operator ofthe vehicle 102 that the tire data indicates an out-of-range condition,such as low tire pressure.

[0029] In FIG. 1, the RF decoder 122 and the controller 124 are shown asseparate elements of the control unit 110. In alternative embodiments,they may be combined in a single processor or logic block or circuit.Any other illustrated elements or additional elements included toenhance the functionality of the system 100 may be integrated orcombined with other components of the system 100.

[0030] Further, the system 100 should not be restricted to use inconjunction with a CAN bus. In alternative embodiments, any othercommunications medium may be employed for interconnecting the system 100with other elements of the vehicle 102. For example, communication busesin accordance with the J-1850 or USB standards may be substituted, orthe control unit 110 may be directly hard wired with other elements ofthe vehicle 102. Still further, external communications may be omittedentirely so that the system 100 is completely self-contained.

[0031]FIG. 1 further shows a detailed view of one embodiment of an RFdetector 112 for use in the remote tire monitor system 100. The RFdetector 112 includes an antenna 140 to sense radio frequency (RF)signals transmitted from the tire monitor 106, an amplifier 142, anenvelope detector coupled to the antenna 140 through the amplifier 142and an output circuit 146 coupled to the envelope detector 144. Theenvelope detector 144 includes a filter 149, a diode 150, a capacitor152 coupled to ground and an amplifier 154. The RF detector 112 ispowered from a power line 156 and a ground line 158 provided on theconductor 114 which couples the RF detector 112 to the input circuit 123of the RF decoder 122. To isolate the operational circuitry of the RFdetector 112 from noise on the power line 156, the RF detector 112further includes a resistor 160 and a capacitor 162 to ground.

[0032] The envelope detector 144 responds to the input signals receivedat the antenna and amplified by the amplifier 142 to produce at theoutput circuit 146 data corresponding to the envelope of the RF signalstransmitted by the tire monitors 106. Thus, the filter 148, diode 150and capacitor 152 together form a circuit coupled with the antenna 140to detect an envelope of electrical signals produced by the antenna inresponse to the RF signals. The envelope is itself an electrical signalwhich is amplified in the amplifier 154. The output signal from theamplifier 154 is applied to the base of a transistor 164. In response tothis signal at its base, the transistor 164 modulates a wireline signalon the conductor 114 in response to the envelope of the RF signalsreceived at the RF detector 112. That is, the signals applied at thebase of the transistor 164 control turn-on of the transistor 164,conducting current from its collector at the power node of the conductor114 to its emitter at the ground node of the conductor 114. As a result,the current in the conductor 114 will be modulated in response to the RFsignals received at the antenna 140 of the RF detector 112.

[0033] In one embodiment, to detect the modulated current, the inputcircuits 123 of the RF decoder in the illustrated embodiment may includea current mirror which duplicates the current drawn from the input stageof the input circuit 123, coupled to the conductor 114. The outputcurrent from the current mirror in the input circuit 123 is provided toa resistor which converts the current signal into a voltage signal whichcan be read by the microcontroller 124. Suitable current mirror circuitsare within the purview of those ordinarily skilled in the art of circuitdesign.

[0034] In this manner, then, the signal provided on the conductor 114forms a transmission indication indicating that the tire monitor 106associated with the RF detector 112 has transmitted an RF signal whichwas detected by the RF detector 112. Producing the transmissionindication includes detecting the envelope of the RF signals transmittedby the tire monitor 106 and producing a wireline signal on the conductor114 in response to the envelope of the RF signals. In particular, in theillustrated embodiment, the wireline signal is produced by modulating acurrent in a conductor 114 coupled with the control unit 110. Thecontrol unit 110 detects the modulation of the current to locate thetransmitting tire monitor 106.

[0035] Significantly, the RF detector 112 does not demodulate the datatransmitted by the tire monitor 106. Only the RF circuit 120 of thecontrol unit 110 demodulates the data to extract the contents of the RFsignal 106. The RF detector only senses the presence of the transmittedRF signals. This reduces the cost of the RF detectors 112 and theoverall cost of the remote tire monitor system 100.

[0036] Also, by modulating the current in the conductor 114, the RFdetector's sensitivity to noise is reduced. Noise will occur in the formof voltage spikes or pulses on the conductor 114. However, this noisewill have little effect on the operation of the RF detector 112 and willhave little effect on the current levels in the conductor. As a result,the conductor 114 can be, for example, a twisted pair of wire or anyother inexpensive two-wire cable. Coaxial cable or other shielded cableis not necessary for implementing the system 100 using RF detector 112.

[0037] In alternative embodiments, the RF circuit 120 may be omitted. Insuch an embodiment, the RF detectors 112 are used to detect thevariations in the radio frequency signals and modulate a wire linesignal on the conductors 114. The RF decoder 122 in such an embodimentis configured to demodulate the data in conjunction with themicrocontroller 124. Current pulses on the conductor 114 are detected bythe RF decoder 122 and converted to voltage pulses. The voltage pulsescan be read by the microcontroller 124. In this manner, microcontroller124 obtains the data from the RF detectors and the RF decoder, withoutuse of an RF circuit 120. This has the advantage of eliminating therelatively expensive RF circuit. Further, this permits reduction in thetransmit power used by the tire monitors 106 to transmit the radiofrequency signals conveying the entire data. In some jurisdictions,substantially attenuated transmit power is required for applicationssuch as tire monitors. These low transmit power requirements may besatisfied while still providing reliable performance in the remote tiremonitoring system 100 by use of the RF detectors 112.

[0038] In still other embodiments, the functionality described hereinmay be implemented using a programmed computer or other processoroperating in response to data and instructions stored in memory. Theprocessor may operate in conjunction with some or all of the hardwareelements described in the embodiments shown herein.

[0039] The disclosed tire monitor system may be used to provide animproved auto learn or auto train method for automatically identifyingpositions of a plurality of tire monitors on a vehicle. As noted above,previously devices such as a transponder or magnetic activation toolswere used in the car plant to train the control unit of the remote tiremonitor system with identifiers for the wheel sensors or tire monitors.With the vehicle located in a training booth or activation area at thefactory, the wheel sensors were activated in sequence and the controlunit, expecting activated pressure transmissions in a certain order,learned the identification and position on the vehicle of the wheelsensors. So as to prevent cross talk from other training booths, eachactivation area is required to be RF shielded. Another method oftraining the receivers was to use bar code readers to scan theidentifiers of the wheel sensors and input this data into the receiver.All of these methods required an additional operation either manually orby automatic readers. These operations add cost and potential fordowntime.

[0040] In the illustrated embodiment of FIG. 1, no such tools arerequired. In the car plant at the end of the production line, a standardone to two minute dynamic test is used to test and calibrate steering,brakes etc. of the vehicle. For the illustrated embodiment, positionsand identities of the four tire pressure monitor wheel sensors areautomatically learned during this dynamic test.

[0041] This is achieved by placing the control unit or receiver in a“learn state” at a dynamic test booth. The wheel sensors transmit eitheronce a minute as in the normal mode, or in a special initial modecorresponding to a brand new, right out of the box state, transmittingmore often, for example every 30 seconds, or every 10 seconds.

[0042] For example, when the wheel sensors leave the manufacturer'sproduction line, they are placed in off mode. This mode means that eachwheel sensor is dormant until it is activated by the closing of itsmotion switch. Closing the motion switch is only achievable throughcentrifugal force caused by spinning the tire monitor on a rotatingwheel. During normal operation, the wheel sensor, while driving,transmits tire information including supervisory tire pressure onceevery minute. However, in the illustrated embodiment, for the drivingperiods during the first 16 activations of the motion switch, the wheelsensor will transmit the supervisory pressure data once every 30 seconds(to conform to United States regulatory requirements) or 10 secondsoutside the United States. Other time intervals may be used. After theinitial 16 transmissions, or any other suitable number, the transmissioninterval is changed to its normal mode value, such as one minute. Thisinitial mode is known as factory test mode.

[0043] At the time of the dynamic vehicle test, the vehicle isaccelerated, causing the wheel sensors to activate with the rotation ofthe wheels and associated closure of their motion switches. When thewheel sensors begin transmitting tire pressure, say once every thirtyseconds, each sensor's identifier is transmitted by the sensor and isreceived up by the RF circuit of the control unit. In this initialunlearned state, the receiver loads the new identifier into memory,associating the transmission with one of the four RF detectors. Onlydata received which also is synchronized to activity on one of the RFdetector conductors is regarded as valid. Over the one to two minuteduration of the dynamic test, each wheel sensor will transmit numeroustimes and the control unit can verify the tire information, such as eachwheel sensor identifier, and associated wheel position. The control unitcan then load this data into non-volatile memory for subsequent normaluse.

[0044] Key advantages of this auto-learn technique is the lack of anyadditional labor or equipment at the vehicle assembly plant, and thelack of a need for a transponder component or magnetic switch in thewheel sensor. Also there is no possibility of learning the wrong wheels,from other vehicles due to cross talk or of getting the wrong position.Thus, cost is reduced, operation is simplified and reliability isincreased. Using the illustrated embodiment of the tire monitor system,no additional activation or learning tools are required to train thecontrol unit with the wheel sensors' position on the vehicle. The onlydevice required to train the control unit is the standard dynamicvehicle test at the end of line test in the vehicle assembly plant.Because the training procedure can be carried out in parallel with thesteering and braking tests on the rolling road, and because of thefactory test mode feature, no extra time or cost is required to ‘autolearn’ the tire monitor system.

[0045] The illustrated embodiment further provides for automatic updateof tire monitor position information in the control unit uponreplacement of one of the tire monitors of the system. This would occur,for example, if one of the wheels or tires of the vehicle is replaced.Due to the nature of the current embodiment, where the RF detectors arecontinuously indicating the position of the wheel sensors, a wheelsensor may be replaced and detected by the control unit without the needfor user intervention. In this case, where a new wheel sensor is put ona wheel, the control unit initially realizes it is receiving a wrongidentifier for the tire monitor, but still getting RF detector pulsesfrom a particular wheel position. In addition, the control unit detectsthat the previously stored identifier for that position is no longerbeing received. Over a period of time, say ten minutes driving, thereceiver verifies it has stopped receiving a stored identifier and isnow receiving a new ID for that position. After verification, the newidentifier is stored for that position and operation continues asnormal.

[0046] The big advantage of this is the lack of need for userintervention and elimination of the need for a service tool at eachservice location. Tire monitor position and identification is updatedautomatically.

[0047]FIG. 2 is a flow diagram illustrating an auto learn method for theremote tire monitor system of FIG. 1. The method begins at block 200. Atblock 202, one or more tires with new tire monitors are mounted on avehicle which includes a remote tire monitor system. In this embodiment,the tire monitors are in unused, out of the box condition from themanufacturer. The installation of block 202 may occur as part of thefinal assembly of the vehicle at the factory. Alternatively, theinstallation may occur when new tires are installed on the vehicle orwhen a remote tire monitor system is added to the vehicle.

[0048] At block 204, the dynamic vehicle test is initiated and, inresponse, at block 206, the tire monitors begin transmitting radiofrequency (RF) signals. The dynamic vehicle test is a test to checkproper functionality of the systems of the vehicle, including drivetrain and brakes. Alternatively, any activity which causes the tiremonitors to begin transmitting may be substituted at block 204 toinitiate transmission at block 206. For example, the process of drivingthe vehicle from the end of the assembly line to a storage area or afinal checkout area in block 204 may be adequate to begin transmissionat block 206. It is contemplated that the tire monitors each include amotion switch which activates the tire monitor in response to motion ofthe tire monitor on the wheel of the vehicle.

[0049] Further, at block 206, the tire monitor begins transmitting at atest mode interval, such as once every 30 or 60 seconds. This aspect maybe omitted but adds convenience for initializing the tire monitorsystem. After initialization, the interval may be reduced to reducepower drain from the battery which powers the tire monitor.

[0050] After transmission of the RF signals at block 206, the RF signalsare received by a receiver of the remote tire monitor system at block208. The RF signals are demodulated, decoded and otherwise processed toextract the data conveyed on the RF signals. For example, the tiremonitor may modulate a carrier signal using data corresponding topressure of the tire or a tire monitor identifier. The receiver of theremote tire monitor system demodulates the received RF signals toreceive the data. At block 212, the data including a tire monitoridentifier, if any, is provided to a control unit of the remote tiremonitor system.

[0051] Meanwhile, the same RF signals received and demodulated at blocks208, 210 are detected at block 214. In the preferred embodiment, the RFsignals are received without demodulation, for example, using a detectorof the type illustrated above in conjunction with FIG. 1. Other suitableRF detectors may be used. At block 216, in response to the detected RFsignals, a transmission indication is provided to the control unit. Thetransmission indication indicates to the control unit which RF detectorof the vehicle detected the RF signals transmitted by the tire monitorand received by the receiver at block 208.

[0052] At block 218, identification information associated with the tiremonitor is stored. In one embodiment, the data forming the identifiertransmitted by the tire monitor and received by the receiver of theremote tire monitor system is stored in memory. Other types and formatsof identification information may be stored. For example, the controlunit may store an RF detector indicator which indicates which RFdetector detected the received RF signals.

[0053] In this manner, the described method provides automatic learncapability in a remote tire monitor system. No manual intervention isnecessary for the control unit to identify and store the identities andlocations of individual tire monitors on the vehicle. This reduces timeand cost associated with initiating operation of the remote tire monitorsystem.

[0054]FIG. 3 is a flow diagram illustrating an auto learn method for theremote tire monitor system of FIG. 1. The method of FIG. 3 starts atblock 300.

[0055] At block 302, RF signals transmitted by a tire monitor associatedwith a wheel of a vehicle are received by a receiver of the remote tiremonitor system. At block 304, the RF signals are demodulated, decodedand otherwise processed to extract the data conveyed on the RF signals.For example, the tire monitor may modulate a carrier signal using datacorresponding to pressure of the tire or a tire monitor identifier. Thetire monitor identifier may be a serial number or other unique ornearly-unique data associated with the tire monitor. For example, thetire monitor identifier may be multiple bit data stored in the tiremonitor at the time of manufacture of the tire monitor. The receiver ofthe remote tire monitor system demodulates the received RF signals toreceive the data. At block 306, the data including a tire monitoridentifier, if any, is provided to a control unit of the remote tiremonitor system.

[0056] Meanwhile, the same RF signals received and demodulated at blocks302, 304 are detected at block 308. In the preferred embodiment, the RFsignals are received without demodulation, for example, using a detectorof the type illustrated above in conjunction with FIG. 1. Other suitableRF detectors may be used. At block 310, in response to the detected RFsignals, a transmission indication is provided to the control unit. Thetransmission indication indicates to the control unit which RF detectorof the vehicle detected the RF signals transmitted by the tire monitorand received by the receiver at block 302.

[0057] At block 312, stored identification information is retrieved frommemory at the control unit. In the illustrated embodiment, theidentification information is stored at a memory location associatedwith the transmission indication or RF detector. Thus, the control unitreceives a wireline indication from a receiving RF detector that atransmission has been received. Using the wireline indication, thecontrol unit selects the memory location from which previousidentification information is retrieved.

[0058] At block 314, the control unit determines if the identifierreceived from the transmitting tire monitor matches the storedidentification information. In this application, a match may mean abit-by-bit match of received and stored data or some other level orassociation between the received data and the stored data. If the datamatch, at block 316, the tire information such as pressure data areupdated. For example, in one embodiment, tire pressure data are storedalong with the identification information for the tire monitor. If thereceived tire pressure data varies by a predetermined amount from thestored tire pressure data, the received tire pressure data is stored andan alarm or other user indication is generated.

[0059] At block 318, if there is no match between the receivedidentifier and the stored identification information, the method waitsfor receipt of an additional transmission associated with this RFdetector. Preferably, the tire monitor transmits pressure data and atire monitor identifier periodically, such as once per minute. Uponreceipt of a subsequent transmission, at block 320, the method attemptsto verify the previously received tire monitor identifier. This is doneby comparing the newly received tire monitor identifier and thepreviously received tire monitor identifier to determine if there was anerror in communication of the previously received tire monitoridentifier. In some embodiments, multiple subsequent transmissions maybe received for comparison. If there is no verification, at block 322,the mismatched transmission received at block 302 is discarded. Thiscondition indicates that the same tire monitor continues to transmit,and the mismatched transmission was received with an error.

[0060] If at block 320 the newly received data verify the previouslyreceived data, the identification information stored for this RFdetector is updated with the tire monitor identifier from the receivedtransmission. This condition indicates that the tire monitor has beenchanged and is communicating reliably. In this manner, the illustratedsystem and method provide automatic update capability after a tiremonitor has been changed. This may occur if the tires of the vehicle arerotated or if one or more tires is replaced. There is thus no need tomanually intervene for the remote tire monitor system to update theidentities and locations of the tire monitors on the vehicle.

[0061] From the foregoing, it can be seen that the present embodimentsprovide a method and apparatus which automatically conveys wheelposition and data to a receiver in a vehicle. Even after changes in tireposition due to tire rotation or replacement of a tire, the systemautomatically re-learns the position of the tires on the vehicle. Noexternal actuation is required. Interference and cross talk areminimized by locating the RF detectors in close proximity to the tiremonitors. The required components are relatively inexpensive and may beimplemented at a relatively low cost. Further, the system providesautomatic learn capability for learning and updating the identities oftire monitors on the vehicle without manual intervention.

[0062] While a particular embodiment of the present invention has beenshown and described, modifications may be made. It is therefore intendedin the appended claims to cover all such changes and modifications whichfall within the true spirit and scope of the invention.

1. A method for operating a remote tire monitor system, the methodcomprising: at a transmitting tire monitor of a plurality of tiremonitors, transmitting radio frequency (RF) signals including tire data;at a RF receiver, receiving the RF signals and detecting the tire data;at a receiving RF detector of a plurality of RF detectors eachassociated with a tire monitor, producing a transmission indication; andat a control unit, receiving the tire data and transmission indicationand associating a position of the transmitting tire monitor with thetire data in response to the transmission indication.
 2. The method ofclaim 1 further comprising: comparing the position of the transmittingtire monitor with a stored position of the transmitting tire monitor;and updating the stored position with the position of the transmittingtire monitor when the position of the transmitting tire monitor differsfrom the stored position.
 3. The method of claim 1 wherein receiving theRF signals comprises: demodulating the RF signals; decoding the tiredata; and conveying the tire data to the control unit.
 4. The method ofclaim 3 wherein decoding the tire data comprises: decoding a tiremonitor identifier; and decoding tire pressure data.
 5. The method ofclaim 1 wherein producing a transmission indication comprises: detectingan envelope of the RF signals; and producing a wire line signal inresponse to the envelope of the RF signals.
 6. The method of claim 5wherein producing a wire line signal comprises: modulating a current ina conductor coupled with the control unit.
 7. The method of claim 6further comprising: detecting modulation of the current at the controlunit to locate the transmitting tire monitor.
 8. A control unit for aremote tire monitor system of a vehicle, the control unit comprising: aradio frequency (RF) receiver configured to receive RF signals conveyingtire data from at least one transmitting tire monitor of a plurality oftire monitors associated with wheels of the vehicle; and a RF decoderconfigured to receive a transmission indication from at least onereceiving RF detector of a plurality of RF detectors associated withwheels of the vehicle and identify a position of the transmitting tiremonitor on the vehicle in response to the transmission indication. 9.The control unit of claim 8 further comprising: a memory; and acontroller configured to store in the memory position of the pluralityof tire monitors including the position of the transmitting tiremonitor.
 10. The control unit of claim 9 wherein the controller isfurther configured to compare the position of the transmitting tiremonitor with a stored position of the transmitting tire monitor storethe position of the transmitting tire monitor as the stored positionwhen the position of the transmitting tire monitor does not match thestored position.
 11. A radio frequency (RF) detector for use inassociation with a tire monitor of a remote tire monitor system of avehicle, the RF detector comprising: an antenna to sense RF signals fromthe tire monitor; an envelope detector coupled to the antenna; and anoutput circuit coupled to the envelope detector.
 12. The RF detector ofclaim 11 wherein the output circuit comprises: at least one transistorto produce a wire line signal.
 13. The RF detector of claim 11 whereinthe envelope detector comprises: a circuit coupled with the antenna todetect an envelope of electrical signals produced by the antenna inresponse to the RF signals; and an amplifier.
 14. The RF detector ofclaim 13 wherein the output circuit comprises: at least one transistorwhich modulates a wire line signal in response to the envelope.
 15. Amethod for a remote tire monitor system, the method comprising:receiving radio frequency (RF) signals including tire data from atransmitting tire monitor associated with a wheel of a vehicle;receiving a wire line indication from an RF detector associated with thetransmitting tire monitor; and identifying position on vehicle of thetransmitting tire monitor in response to the wire line indication. 16.The method of claim 15 further comprising: storing position data for aplurality of tire monitors of the remote tire monitor system; andupdating the position data for the transmitting tire monitor when theposition of the transmitting tire monitor varies from a stored positionfor the transmitting tire monitor.
 17. The method of claim 15 whereinreceiving a wire line indication comprises: detecting a modulatedelectrical signal on a wire coupled to the RF detector near thetransmitting tire monitor.
 18. The method of claim 17 wherein detectinga modulated electrical signal comprises: detecting current which hasbeen modulated by an envelope of the RF signals at the RF detector. 19.A remote tire monitor system comprising: a plurality of tire monitors,each tire monitor being associated with a wheel of a vehicle andconfigured to transmit radio frequency (RF) signals including tire data;a plurality of RF detectors, each RF detector being mounted on thevehicle proximate an associated tire monitor to detect the RF signalsfrom the associated tire monitor and produce a transmission indicationin response to detected RF signals; a RF receiver to receive tire datain RF signals transmitted by any tire monitor of the plurality of tiremonitors; and a control unit coupled with the plurality of RF detectorsto receive transmission indications and coupled with the RF receiver toreceive the tire data, the control unit being operative to associate aposition of a transmitting tire monitor with a received transmissionindication.
 20. The remote tire monitor system of claim 19 wherein eachRF detector comprises: an envelope detector to detect an envelope of theRF signals from the associated tire monitor; and an output circuit tomodulate an electrical signal on a conductor as the transmissionindication.
 21. The remote tire monitor system of claim 20 wherein theoutput circuit comprises: at least one transistor for modulating acurrent in the conductor.
 22. A method for automatically identifyingpositions of a plurality of tire monitors on a vehicle, the methodcomprising: initiating operation of the plurality of tire monitors uponoperation of the vehicle; receiving from the plurality of tire monitorsradio frequency (RF) signals containing tire information; receivingwireline indications from a plurality of RF detectors, each RF detectorbeing associated on the vehicle with a tire monitor to detect but notdemodulate RF signals transmitted by the tire monitor; and associatingthe tire information from each tire monitor with an RF detector inresponse to the wireline indications.
 23. The method of claim 22 furthercomprising: at each tire monitor, detecting motion of the tire monitor;and transmitting local tire information in response to detection ofmotion.
 24. The method of claim 23 wherein transmitting local tireinformation comprises: transmitting tire pressure data.
 25. The methodof claim 24 wherein transmitting local tire information furthercomprises: transmitting a tire monitor identifier associated with thetire monitor.
 26. The method of claim 22 wherein associating the tireinformation from each tire monitor with an RF detector comprisesdetermining an identifier associated with a transmitting tire monitor inthe tire information; identifying a receiving RF detector whichoriginated a received wireline indication; and storing the identifier ata memory location associated with the receiving RF detector.
 27. Themethod of claim 22 further comprising: receiving subsequent RF signalscontaining additional tire information; receiving subsequent wirelineindications from receiving RF detectors; associating the additional tireinformation with the receiving RF detectors; and verifying the tireinformation with the additional tire information.
 28. The method ofclaim 27 further comprising: after verification, storing the tireinformation in a memory location associated with the RF detector whichis associated with the tire information.
 29. A method for automaticallyupdating a remote tire monitor system of a vehicle, the methodcomprising: storing identification information for each tire monitor ofa plurality of tire monitors of the vehicle; receiving an identifiertransmitted by a transmitting tire monitor; receiving a transmissionindication from a receiving radio frequency (RF) detector associatedwith the transmitting tire monitor; and when the identifier does notproduce a match with the identification information, updating theidentification information using the identifier.
 30. The method of claim29 wherein receiving the identifier comprises: receiving RF signals atan RF circuit; demodulating the RF signals to receive tire information;and locating the identifier in the tire information.
 31. The method ofclaim 30 wherein receiving a transmission indication comprises:detecting the RF signals at the receiving RF detector; and withoutdemodulating the RF signals, producing a wireline indication in responseto the RF signals; and at a control unit, detecting the wirelineindication as the transmission indication.
 32. The method of claim 31further comprising: in response to the wireline indication, reading theidentification information from a storage location in memory, thestorage location being associated with the receiving RF detector.